The present invention relates to surgical devices and relates more particularly to a banding assembly for applying a clamp to close the split halves of the sternum incident surgery that involves a median sternotomy, e.g., open heart surgery.
For proper healing of the split sternum to occur the surgically opened faces must be approximated, compressed and held together rigidly. This task is complicated by the physiological role of the sternum. It is a functional component of the thoracic cage and, with the costal cartilages, serves as the hinge for the "bucket handle" action of the ribs during respiration. The incessant motion of the rib cage transmits continuous stresses across the sternum. Any method for closing the split sternum must be able to maintain compression and rigidity across the closure in the face of these constant stresses.
One commonly used technique closes the sternum with interrupted stainless steel wires. Five or six 20 gauge stainless steel wires are placed either parasternally (around the sternum) or transternally (through the sternum) using a large, swaged-on cutting needle. The needles are cut off and the sternal halves are approximated by twisting the wires. Finally the wires are cut short and the ends are tucked into the adjacent tissue. While this is a useful surgical technique for closing the sternum, there are certain problems associated with this procedure. The wires are difficult to place and if to be placed transternally, the needle must be driven through the sternum, a physically very difficult task. The internal mammary artery can be easily injured when the wires are placed in the parasternal position by the cutting needles which are usually used although tapered needles would be more appropriate in this location. The internal mammary artery passes in close proximity to the area in the intercostal space through which the parasternal wire is passed and injuries to the internal mammary artery are not unusual following the use of cutting needles in this area. Also sharp wires can cause cutting of surgical gloves and injure the operator. Cutting the needle off of the wire creates a sharp point at the end of the wire. The presence of 10 to 14 of these sharp points in a field crowded with hand motion inevitably results in a certain number of cut gloves and also cut fingers with resultant risks to both patient and operator.
An additional problem is that the stress during twisting produces torsional stresses that severely weaken the wire and they often break during their application as they are given that final extra twist used to make the closure "extra snug." The stresses imparted by respiratory motion of the chest cage can further fatigue the wires and cause them to break during the post-operative period. Further, the ends of the twisted wires can often be felt by the patient below the skin. This can be a source of discomfort and concern for the patient. In the most extreme case of the problem the wires cause a mechanical irritation on the skin that can progress to the point where they actually erode through the skin and become infected. When this happens, the wires must be surgically removed.
A major disadvantage of using wires is that they can slice through thin or osteoporotic bone. When sternal wires are used in those older or female patients who have thin or osteoporotic bone they have a tendency to slice through the bone. The large amount of force that the wire applies over its small surface area causes the wire to crush the underlying bone. This occurs during the tightening of the wire and continues during each respiratory cycle until the tension on the wire is eased. When this happens the compression of the sternal closure rigidity is lost.
Finally it should be noted that closure of the sternum with wires is a slow and tedious technique.
Other techniques for closing the sternum have been proposed. For example, U.S. Pat. No. 4,583,541 while still employing wire banding, positions a board at the front of the sternum through which the wires are passed before knotting and the knots are placed in a groove in the board. U.S. Pat. No. 4,279,248 discloses use of C-shaped clamp placed at both sides of the sternum which are clamped together with a threaded screw passing through the sternum, the clamps biting into the bone to provide firm sternum halves closure. U.S. Pat. No. 4,201,215 discloses use of a two-piece C-shaped clamp at one side of the sternum, the clamp pieces having hook ends which pass around to the other side of the sternum. The clamp pieces are assembled and slid tight in opposite directions and crimped together to provide clamp together of the two parts of the sternum. The clamping pieces may be provided with tongue and recess means to lock them in a clamp position and the clamp pieces are then crimped together. Tools such as vise grip pliers must be used in this procedure to effect clamp crimping. U.S. Pat. No. 3,802,438 discloses sternum closure with wires in conjunction with a splice plate in which the wires are received. By use of special tools, the splice plate is deformed to anchor the wires therein and in the course of which the sternum is closed. The procedures and devices disclosed in these patents mitigate to a certain extent the problems discussed earlier such as perhaps those associated with patient discomfort caused by twisted wire ends. But they still rely on use of wires and because of the potential for wires to slice or invade the sternum and adjacent tissue structure it is easy to understand that sternum closure without employment of wires is to be preferred.
The sternal banding technique was developed to avoid some of the drawbacks of wire closure. Thus stainless steel bands popularly known as "Parham" bands have been used for closing the sternum as have nylon bands similar to the surgical bands disclosed in U.S. Pat. No. 4,119,091. But these forms of banding possess their own particular shortcomings.